As I see it right now, the defense needs to explain the presence of the positive evidence in the RV in order to be certain of getting a not guilty vote.
Putting all the eggs in the basket of a bug guy is too big a chance.
If kids did play in the RV finding at least one kid who played in the RV must not be that hard to do.
On the other side, I agree that the prosecution needs to provide at least an alternate theory to respond to the bug guys. My guess will be that he'll approach it two-fold. On the one hand he will attempt to find an alternate way of coming up with the same life cycles as the bug guys but it will be based a later start date due to weather.
I also guess he will attempt to establish some other evidence that puts the date earlier than the bug guys, possibly some connection to the animal's, rain or something else that provides a way for the juror to accept an earlier dump date.
If the prosecutor doesn't even offer a fig leaf I would assme a hung jury. Because of the unexplained positive evidence in the RV I don't see the jury coming back with a not guilty, the best they would do is a hung jury.